The invention relates to a surgical instrument with at least two distal jaw parts actuatable commonly and in opposite directions in a pivotingly movable manner by a pull-push rod, whose movement is guided by a sliding block guide consisting of a groove arranged in the jaw parts and a groove block engaging into the groove, wherein each jaw part on the proximal side comprises a circular arc shaped groove which in jaw parts neighboring one another are each arranged displaced by 180.degree..
Such a surgical instrument is known for example from the U.S. Pat. No. 4,887,612. With this instrument the jaw parts are each pivotable commonly and in opposite directions about a journal bearing, as a point of rotation, lying on the longitudinal axis of the instrument. Since the section line of the force exerted by the pull-push rod goes through this journal bearing serving as a pivoting bearing of the two jaw parts and also through the groove block common to both annular grooves, no reduction in force of the movement of the jaw parts with the pull-push rod is possible.
The U.S. Pat. No. 4,712,545 describes a surgical instrument with which for the pivoting movement of a single pivotable jaw part a virtual point of rotation lying outside the shank is formed by a sliding block guide so that here a reduction in force on moving the movable jaw part is achieved. However with this solution known from this US patent only instruments with a single movable jaw part may be realised. This is due to the fact that the grooves are incorporated in the inner flanks of the outer jaw part and the outer flanks of the inner jaw part. Furthermore the grooves and guides can only be manufactured with difficulty which increases the cost of manufacture.